The invention provides a novel solution to the problems posed by conventional conveyor systems such as continuous belts or chains used in the conveying of various items during manufacturing procedures.
The use of continuous chain or belt drives suffers from a fundamental disadvantage in that all procedures or operations which are undertaken to items conveyed must be done simultaneously. A clutch system is often used to remove items from a continuously moving conveyor, however, items are jolted when re-engaged or disengaged from the conveyor. If the belt breaks or if an operation is shut down for any reason, in general, the entire belt must be stopped and all operations along its length are curtailed until operation is resumed.
For example, a common application of a continuous chain conveyor is in the preparation, painting and drying of sheet metal parts. An overhead chain is often used which has hooks suspending below the chain on which sheet metal parts are hung. Once the items have been manually hung up on a hook of the chain, while the chain is moving, the parts may be dipped in a degreasing compound, then dried, passed through a spray painting booth where they are coated, passed through a drying oven and thereafter removed from the hooks and packed or forwarded for further assembly.
The disadvantage of using conventional chain conveyors is that the timing of all manufacturing steps along the processes are determined by the speed of the chain. For example, if one wished to use a slow drying paint which required a longer residence time in an oven, the chain speed must be reduced or the length of the oven extended in order to extend the drying time. Likewise if any step in the procedure, such as hanging parts manually, becomes the determining factor, the only way to speed up production is to put more workers on the slowest operation.
Optimization of a single particular operation is often not possible without a complete optimization of the entire manufacturing procedure.
Therefore although the mechanics of a continuous chain drive conveyor system are relatively straight forward, the design and modification of manufacturing procedures along such a continuous conveyor are severely disadvantaged by requiring all operations to be determined by the speed of the chain. It is generally not possible to stop one portion of the operation without stopping the entire conveyor system. Likewise it is difficult to increase or reduce speed of a particular operation without affecting all other operations along the continuous conveyor.
Maintenance of a continuous conveyor is also at a disadvantage since if one portion of the conveyor system malfunctions the entire system often must be shut down.
Chain drive continuous conveyors often include means to connect or disconnect a item to be conveyed from the chain. For example a lever may be strung to maintain an item in a stationary position as the chain slides through a sleeve or a clutch. However when one wishes to recommence movement of the conveyed item, the items are jolted or jerked together. Such jolting may cause a safety hazard to operating personnel and may cause the conveyed items suspended from the chain to impact against each other. Such impacts may chip paint and produce undesirable dents or other damage.
A further disadvantage of using chain drive conveyor systems through drying ovens is that it is essentially impossible to seal the oven when moving parts must be constantly inserted and withdrawn from the oven on a moving chain drive. A common configuration simply leaves the entrance and exit doors open resulting in excessive fuel consumption. In order to save fuel it is possible to remove items from the chain and insert them into a closed oven however the extra handling involved in such an operation does not counterbalance the savings in fuel expense generally.
In particular such conveyor systems supplied to painting operations raise further disadvantages. When electrostatic coating systems are used it is essential that the chain be grounded at all times despite the fact that it is moving. Since the chain must be adequately lubricated as well, a fundamental disadvantage is presented since proper lubrication and maintenance of a good ground to ensure high quality electrostatic coating are incompatible.
Electrostatic powder coating is becoming the norm for coating technologies since no solvents are required and oversprayed powder may be recycled thereby saving expense and substantially eliminating pollution problems.
Electrostatic powder coating booths are relatively expensive and in order to change colours or other paint characteristics it is necessary to meticulously clean the booth to avoid contamination between different paint types. The cost of powder paint booths therefore is relatively high since they must be specifically designed to be easily cleaned and to withstand several cleanings. It is common to construct powder paint booths out of stainless steel for these reasons. For example it is not unusual for the change over from one paint colour to another to involve a one half a day of cleaning of the paint booth before the change over can be completed.
It will be apparent therefore that relatively long runs of a particular colour paint are desirable to maximize production efficiency. The change over of colours or other paint types to accommodate short runs is impractical because of the time and cost involved in cleaning the paint booths every time a paint type must be changed.